Process for the hydrodesulfurization of sulfur-containing olefinic gasoline cuts using a regenerated catalyst

ABSTRACT

The invention relates to a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of between 200° C. and 400° C., a total pressure of between 1 and 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of between 1 and 10 h −1 ; and a hydrogen/gasoline feedstock ratio by volume of between 100 and 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut and comprises at least one metal from group VIII, at least one metal from group VIb and an oxide support.

FIELD OF THE INVENTION

The present invention relates to a process for the hydrodesulfurization of a gasoline cut employing a regenerated catalyst.

STATE OF THE ART

Sulfur is an element naturally present in crude oil and is thus present in gasoline and diesel fuel if it is not removed during refining. However, sulfur in gasoline interferes with the efficiency of emission reduction systems (catalytic converters) and contributes to air pollution. In order to combat environmental pollution, all countries are consequently gradually adopting strict sulfur specifications, the specifications being, for example, 10 ppm (weight) of sulfur in commercial gasolines in Europe, China, the United States and Japan. The problem of reducing sulfur contents is essentially focused on gasolines obtained by cracking, whether catalytic (FCC, Fluid Catalytic Cracking) or noncatalytic (coking, visbreaking, steam cracking), the main precursors of sulfur in gasoline pools.

One solution, well known to a person skilled in the art, for reducing the sulfur content consists in carrying out a hydrotreating (or hydrodesulfurization) of the hydrocarbon cuts (and in particular of catalytic cracking gasolines) in the presence of hydrogen and of a heterogeneous catalyst. However, this process exhibits the major disadvantage of causing a very significant drop in the octane number if the catalyst employed is not sufficiently selective. This reduction in the octane number is linked in particular to the hydrogenation of the olefins present in this type of gasoline concomitantly with the hydrodesulfurization.

Unlike other hydrotreating processes, in particular those for feedstocks of gas oil type, the hydrodesulfurization of gasolines thus has to make it possible to respond to a double antagonistic constraint: to provide extreme hydrodesulfurization of gasolines and to limit the hydrogenation of the unsaturated compounds present.

The most widely used route for responding to the double problem mentioned above consists in employing processes in which the sequence of unit stages makes it possible simultaneously to maximize the hydrodesulfurization while limiting the hydrogenation of the olefins. Thus, the most recent processes, such as the Prime G+ (trademark) process, make it possible to desulfurize cracked gasolines rich in olefins, while limiting the hydrogenation of the mono-olefins and consequently the loss of octane and the high hydrogen consumption which results therefrom. Such processes are, for example, described in the patent applications EP 1 077 247 and EP 1 174 485.

Obtaining the desired reaction selectivity (ratio of hydrodesulfurization to hydrogenation of olefins) can thus be partly due to the choice of the process but, in all cases, the use of an intrinsically selective catalytic system is very often a key factor. In general, the catalysts used for this type of application are catalysts of sulfide type containing an element from group VIb (Cr, Mo, W) and an element from group VIII (Fe, Ru, Os, Co, Rh, Ir, Pd, Ni, Pt). Thus, in the U.S. Pat. No. 5,985,136, it is claimed that a catalyst exhibiting a surface concentration of between 0.5×10⁻⁴ and 3×10⁻⁴ g of MoO₃/m² makes it possible to achieve high selectivities in hydrodesulfurization (93% hydrodesulfurization (HDS) against 33% hydrogenation of olefins (HOO)). Furthermore, according to the U.S. Pat. Nos. 4,140,626 and 4,774,220, it can be advantageous to add a dopant (alkali metal, alkaline earth metal) to the conventional sulfide phase (CoMoS) with the aim of limiting the hydrogenation of olefins. The documents U.S. Pat. No. 8,637,423 and EP 1 892 039, which describe selective hydrodesulfurization catalysts, are also known in the state of the art.

During its use for the hydrotreating of a petroleum cut, a hydrotreating catalyst experiences a decrease in its activity due to the deposition of coke and/or of compounds which are sulfur-based or contain other heteroelements. Beyond a certain period, its replacement is thus necessary. In particular, the tightening of the sulfur specifications of fuels induces an increase in the frequency of replacement of the catalyst, which leads to an increase in the cost associated with the catalyst and to an increase in the amount of spent catalyst.

In order to combat these disadvantages, the regeneration (gentle calcination) of catalysts for the hydrodesulfurization of middle distillates (gas oil) or of spent residues is an economically and ecologically advantageous process because it makes it possible to use these catalysts again in industrial units rather than to landfill them or to recycle them (recovery of the metals). However, the regenerated catalysts are generally less active than the starting solids. Thus, the patent application US2011/0079542 indicates that, after regeneration, a typical commercially available catalyst for the hydrotreating of distillates can have a reactivity from approximately 75% to approximately 90% of the activity of the corresponding fresh catalyst.

In order to solve this problem, these regenerated catalysts are generally additivated with various organic agents (“rejuvenation” stage) in the field of middle distillates. Many patents, such as, for example, U.S. Pat. Nos. 7,906,447, 8,722,558, 7,956,000, 7,820,579 or also CN102463127, thus provide different methods for carrying out the rejuvenation of the catalysts for the hydrotreating of middle distillates. Catalysts for the hydrodesulfurization of middle distillates, which have high contents of metals in comparison with the catalysts for the selective hydrodesulfurization of gasolines, experience significant sintering during use and during regeneration. Thus, the rejuvenation treatments are focused on the dissolution and the redistribution of the metal phases in order to recover a dispersion close to the fresh catalyst and therefore an activity close to the fresh catalyst.

Catalysts for the selective hydrodesulfurization of gasolines exhibit different regeneration issues from catalysts for the hydrotreating of gas oils, in particular due to the need to maintain the selective nature of the catalyst with respect to reactions for hydrodesulfurization and hydrogenation of olefins. This is because an increase in the selectivity is generally more desirable than an increase in or maintenance of the activity in the field of gasolines. As regards the selective hydrodesulfurization of gasolines, while the conventional regeneration can be envisaged, a person skilled in the art, in view of what has been demonstrated for the catalysts for the hydrotreating of middle distillates, expects the catalyst to exhibit a significantly lower activity than that of the fresh catalyst and with a potentially reduced selectivity, due to the structural changes in the active phase supported on the catalyst during the regeneration.

There thus still exists today a keen interest among refiners for processes for the hydrodesulfurization in particular of gasoline cuts which exhibit good catalytic performance qualities, in particular in terms of catalytic activity in hydrodesulfurization and of selectivity, making possible the employment of catalysts resulting from spent hydrotreating catalysts.

Subject Matters of the Invention

The invention thus relates to a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of between 200° C. and 400° C., a total pressure of between 1 and 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of between 1 and 10 h⁻¹; and a hydrogen/gasoline feedstock ratio by volume of between 100 and 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, said regenerated catalyst comprises at least one metal from group VIII, at least one metal from group VIb and an oxide support.

This is because it has been observed that the use of a regenerated catalyst in a process for the selective hydrodesulfurization of gasolines only resulted in a very small loss in activity compared with the use of the same fresh catalyst and surprisingly brought about an improvement in the selectivity. Without being committed to any theory, it seems that the changes with regard to the active phase caused by the regeneration of the catalyst and bringing about a better selectivity toward the hydrodesulfurization reaction of the active sites make it possible to compensate for the reduction in the number of these sites and thus maintain the activity of the catalyst.

According to one alternative form, the regenerated catalyst has a content of metal from group VIb of between 1% and 20% by weight of oxide of said metal from group VIb, with respect to the total weight of the regenerated catalyst, and a content of metal from group VIII of between 0.1% and 10% by weight of oxide of said metal from group VIII, with respect to the total weight of the regenerated catalyst.

According to one alternative form, the regenerated catalyst additionally contains phosphorus, the phosphorus content being between 0.3% and 10% by weight, expressed as P₂O₅, with respect to the total weight of the regenerated catalyst and the phosphorus/(metal from group VIb) molar ratio in the regenerated catalyst is between 0.1 and 0.7.

According to one alternative form, the metal from group VIb is chosen from tungsten and molybdenum and the metal from group VIII is chosen from nickel and cobalt in the regenerated catalyst.

According to one alternative form, the regenerated catalyst is characterized by a specific surface of between 20 and 200 m²/g, preferably of between 30 and 180 m²/g.

According to one alternative form, the oxide support of the regenerated catalyst is chosen from aluminas, silica, silica-aluminas or also titanium or magnesium oxides, used alone or as a mixture with alumina or silica-alumina.

According to one alternative form, the regenerated catalyst contains residual carbon at a content of less than 2% by weight, with respect to the total weight of the regenerated catalyst.

According to one alternative form, the regenerated catalyst contains sulfur at a content of less than 5% by weight, with respect to the total weight of the regenerated catalyst.

According to one alternative form, the regenerated catalyst is subjected to a sulfidation stage before or during the hydrodesulfurization process.

According to one alternative form, the gasoline cut is a gasoline resulting from a catalytic cracking unit.

According to one alternative form, the regenerated catalyst results from a regeneration stage carried out in an oxygen-containing gas stream carried out at a temperature of between 350° C. and 550° C.

According to one alternative form, the regeneration stage is preceded by a deoiling stage which comprises bringing an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut into contact with a stream of inert gas at a temperature of between 300° C. and 400° C.

According to one alternative form, the regenerated catalyst does not undergo addition of metals from groups VIb and/or VIII, of phosphorus and/or of organic compound after the regeneration stage.

According to one alternative form, the process is carried out in a catalytic bed of a reactor of the fixed bed type containing several catalytic beds; at least one other catalytic bed upstream or downstream of the catalytic bed containing the regenerated catalyst in the direction of the circulation of the feedstock contains at least in part a fresh catalyst and/or a rejuvenated catalyst.

According to another alternative form, the process is carried out in at least two reactors in series of the fixed bed type or of the ebullated bed type; at least one of the reactors contains a regenerated catalyst while another reactor contains a fresh catalyst or a rejuvenated catalyst, or a mixture of a regenerated catalyst and of a fresh and/or rejuvenated catalyst, in any order, with or without removal of at least a part of the H₂S from the effluent resulting from the first reactor before treating said effluent in the second reactor.

Subsequently, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, published by CRC Press, editor D. R. Lide, 81^(st) edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals from columns 8, 9 and 10 according to the new IUPAC classification.

DESCRIPTION OF THE INVENTION

The invention thus relates to a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of between 200° C. and 400° C., a total pressure of between 1 and 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of between 1 and 10 h⁻¹; and a hydrogen/gasoline feedstock ratio by volume of between 100 and 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, said regenerated catalyst comprises at least one metal from group VIII, at least one metal from group VI b and an oxide support.

The hydrodesulfurization process according to the invention makes it possible to transform the organosulfur compounds of a gasoline cut into hydrogen sulfide (H₂S) while limiting as much as possible the hydrogenation of the olefins present in said cut.

Feedstock to be Treated

The process according to the invention makes it possible to treat any type of sulfur-containing olefinic gasoline cut, such as, for example, a cut resulting from a coking, visbreaking, steam cracking or catalytic cracking (FCC, Fluid Catalytic Cracking) unit. This gasoline can optionally be composed of a significant fraction of gasoline originating from other production processes, such as atmospheric distillation (gasoline resulting from a direct distillation (or straight run gasoline)), or from conversion processes (coking or steam cracking gasoline). Said feedstock preferably consists of a gasoline cut resulting from a catalytic cracking unit.

The feedstock is a sulfur-containing olefinic gasoline cut, the boiling point range of which typically extends from the boiling points of the hydrocarbons having 2 or 3 carbon atoms (C2 or C3) up to 260° C., preferably from the boiling points of the hydrocarbons having 2 or 3 carbon atoms (C2 or C3) up to 220° C., more preferably the boiling points of the hydrocarbons having 5 carbon atoms up to 220° C. The process according to the invention can also treat feedstocks having lower end points than those mentioned above, such as, for example, a C5-180° C. cut.

The sulfur content of the gasoline cuts produced by catalytic cracking (FCC) depends on the sulfur content of the feedstock treated by the FCC, the presence or not of a pretreatment of the feedstock of the FCC, as well as on the end point of the cut. Generally, the sulfur contents of the whole of a gasoline cut, in particular those originating from the FCC, are greater than 100 ppm by weight and most of the time greater than 500 ppm by weight. For gasolines having end points of greater than 200° C., the sulfur contents are often greater than 1000 ppm by weight; they can even, in certain cases, reach values of the order of 4000 to 5000 ppm by weight.

In addition, the gasolines resulting from catalytic cracking (FCC) units contain, on average, between 0.5% and 5% by weight of diolefins, between 20% and 50% by weight of olefins and between 10 ppm and 0.5% by weight of sulfur, generally less than 300 ppm of which of mercaptans. The mercaptans are generally concentrated in the light fractions of the gasoline and more specifically in the fraction, the boiling point of which is less than 120° C.

It should be noted that the sulfur compounds present in the gasoline can also comprise heterocyclic sulfur compounds, such as, for example, thiophenes, alkylthiophenes or benzothiophenes. These heterocyclic compounds, unlike mercaptans, cannot be removed by extractive processes. These sulfur compounds are consequently removed by a hydrotreating, which leads to their transformation into hydrocarbons and H₂S.

Preferably, the gasoline treated by the process according to the invention is a heavy gasoline (or HCN for Heavy Cracked Naphtha) resulting from a distillation stage aimed at separating a broad cut of the gasoline resulting from a cracking process (or FRCN for Full Range Cracked Naphtha) into a light gasoline (LCN for Light Cracked Naphtha) and a heavy gasoline HCN. The cut point of the light gasoline and of the heavy gasoline is determined in order to limit the sulfur content of the light gasoline and to make it possible to use it in the gasoline pool, preferably without additional post-treatment. Advantageously, the broad cut FRCN is subjected to a selective hydrogenation stage described below before the distillation stage.

Regenerated Catalyst

The regenerated catalyst used in the process according to the invention results from an at least partially spent catalyst, itself resulting from a fresh catalyst, which has been used in a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut under the conditions as described below for a certain period of time and exhibits a significantly lower activity than the fresh catalyst, which necessitates its replacement.

The fresh catalyst comprises at least one metal from group VIII, at least one metal from group VIb, an oxide support and optionally phosphorus. The fresh catalyst can also additionally comprise at least one organic compound containing oxygen and/or nitrogen and/or sulfur before sulfidation.

According to another alternative form, the fresh catalyst does not comprise phosphorus.

The preparation of the fresh catalyst is known and generally comprises a stage of impregnation of the metals from group VIII and from group VIb and optionally of phosphorus and/or of the organic compound on the oxide support, followed by a drying operation, then by an optional calcination making it possible to obtain the active phase in their oxide forms. Before its use in a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, the fresh catalyst is generally subjected to a sulfidation in order to form the active entity as described below.

According to an alternative form of the invention, the fresh catalyst has not undergone calcination during its preparation, that is to say that the impregnated catalytic precursor has not been subjected to a stage of heat treatment at a temperature of greater than 200° C. under an inert atmosphere or under an oxygen-containing atmosphere, in the presence or absence of water.

According to another alternative form of the invention, which is preferred, the fresh catalyst has undergone a calcination stage during its preparation, that is to say that the impregnated catalytic precursor has been subjected to a stage of heat treatment at a temperature of between 200° C. and 1000° C. and preferably between 350° C. and 750° C., for a period of time typically of between 15 minutes and 10 hours, under an oxygen-containing atmosphere, in the presence or absence of water. This is because it has been noticed that a regenerated catalyst resulting from a fresh catalyst which has undergone a calcination stage during its preparation shows a less pronounced fall in activity than a regenerated catalyst resulting from a fresh catalyst which has not undergone a calcination stage during its preparation.

During the process for the hydrodesulfurization of the sulfur-containing olefinic gasoline cut, coke and sulfur, and also other contaminants resulting from the feedstock, such as silicon, arsenic and chlorine, are formed and/or deposited on the catalyst and convert the fresh catalyst into an at least partially spent catalyst.

An at least partially spent catalyst is understood to mean a catalyst which exits from a process for the hydrodesulfurization of the sulfur-containing olefinic gasoline cut carried out under the conditions as described below and which has not undergone a heat treatment under a gas containing air or oxygen at a temperature of greater than 200° C. It may have undergone a deoiling.

It should be noted that the term “coke” or “carbon” in the present patent application denotes a substance based on hydrocarbons which is deposited on the surface of the catalyst during its use, which is highly cyclized and condensed and which has a similar appearance to graphite.

The at least partially spent catalyst contains in particular carbon at a content generally of greater than or equal to 2% by weight, preferably of between 2% and 10% by weight and more preferably still of between 2.2% and 6% by weight, with respect to the total weight of the at least partially spent catalyst.

The process for the regeneration of the at least partially spent catalyst used to generate the regenerated catalyst employed in the process according to the invention comprises a stage of removal of the coke and sulfur (regeneration stage), generally preceded by a deoiling stage.

Even if this is possible, the regeneration is preferably not carried out by keeping the laden catalyst in the hydrodesulfurization reactor (in situ regeneration). Preferably, the at least partially spent catalyst is thus extracted from the reactor and sent to a regeneration plant in order to carry out the regeneration in said plant (ex situ regeneration).

The deoiling stage generally comprises bringing the at least partially spent catalyst into contact with a stream of inert gas (that is to say essentially devoid of oxygen), for example in a nitrogen atmosphere or the like, at a temperature of between 300° C. and 400° C., preferably of between 300° C. and 350° C. The inert gas flow rate in terms of flow rate per unit volume of the catalyst is from 5 to 150 SI·I⁻¹·h⁻¹ for 3 to 7 hours.

In an alternative form, the deoiling stage can be carried out by light hydrocarbons, by steam treatment or any other analogous process.

The regeneration stage is generally carried out in a gas stream containing oxygen, generally air. The water content is generally between 0% and 50% by weight. The gas flow rate in terms of flow rate per unit volume of the spent catalyst is preferably from 20 to 2000 SI·I⁻¹·h⁻¹, more preferably from 30 to 1000 SI·I⁻¹·h⁻¹ and particularly preferably from 40 to 500 SI·I⁻¹·h⁻¹. The duration of the regeneration is preferably 2 hours or more, more preferably 2.5 hours or more and particularly preferably 3 hours or more. The regeneration of the at least partially spent catalyst is generally carried out at a temperature of between 350° C. and 550° C., preferably of between 360° C. and 500° C.

The regenerated catalyst obtained in the regeneration stage contains residual carbon at a content preferably of less than 2% by weight, preferably of between 0.1% and 1.9% by weight, with respect to the total weight of the regenerated catalyst, preferentially of between 0.1% and 1.5% by weight and particularly preferably between 0.1% and 1.0% by weight. The regenerated catalyst may also not contain residual carbon.

It should be noted that the term “residual carbon” in the present patent application means carbon (coke) remaining in the regenerated catalyst after regeneration of the at least partially spent catalyst. This residual carbon content in the regenerated catalyst is measured by elemental analysis according to ASTM D5373.

The regenerated catalyst obtained in the regeneration stage contains residual sulfur (before the optional sulfidation) at a content of less than 5% by weight, preferably of between 0.1% and 4.9% by weight, with respect to the total weight of the regenerated catalyst, preferentially of between 0.1% and 2.0% by weight and particularly preferably between 0.2% and 0.8% by weight. The regenerated catalyst may also not contain residual sulfur. This residual sulfur content in the regenerated catalyst is measured by elemental analysis according to ASTM D5373.

The regenerated catalyst of the process according to the invention is generally composed of the oxide support, of the active phase formed of at least one metal from group VIb and of at least one metal from group VIII and optionally of the phosphorus of the fresh catalyst.

The contents of metal from group VIb, of metal from group VIII and of phosphorus in the fresh, at least partially spent or regenerated catalyst are expressed as oxides after correction for the loss on ignition of the catalyst sample in a muffle furnace at 550° C. for two hours. The loss on ignition is due to the loss of moisture, carbon, sulfur and/or other contaminants. It is determined according to ASTM D7348.

The contents of metal from group VIb, of metal from group VIII and optionally of phosphorus in the regenerated catalyst are substantially identical to the contents of the at least partially spent catalyst from which it results.

The contents of metal from group VIb, of metal from group VIII and optionally of phosphorus in the at least partially spent catalyst are substantially identical to the contents of the fresh catalyst from which it results.

The regenerated catalyst used in the hydrodesulfurization process according to the invention is in particular non-additivated, that is to say that it does not contain an organic compound introduced after its regeneration. Furthermore, no addition of metals from groups VIb and/or VIII or of phosphorus is carried out after the regeneration stage.

The metal from group VIb present in the active phase of the regenerated catalyst is preferentially chosen from molybdenum and tungsten. The metal from group VIII present in the active phase of the regenerated catalyst is preferentially chosen from cobalt, nickel and the mixture of these two elements. The active phase of the regenerated catalyst is preferably chosen from the group formed by the combination of the elements nickel-molybdenum, cobalt-molybdenum and nickel-cobalt-molybdenum, and very preferably the active phase consists of cobalt and molybdenum.

The content of metal from group VIII is between 0.1% and 10% by weight of oxide of the metal from group VIII, with respect to the total weight of the regenerated catalyst, preferably of between 0.6% and 8% by weight, preferably of between 2% and 7%, very preferably of between 2% and 6% by weight and more preferably still of between 2.5% and 6% by weight.

The content of metal from group VIb is between 1% and 20% by weight of oxide of the metal from group VIb, with respect to the total weight of the regenerated catalyst, preferably of between 2% and 18% by weight, very preferably of between 3% and 10% by weight of oxide.

The metal from group VIII to metal from group VIb molar ratio of the regenerated catalyst is generally between 0.15 and 1.15, preferably between 0.19 and 0.8.

In addition, the regenerated catalyst exhibits a density of metal from group VIb, expressed as number of atoms of said metal per unit area of the catalyst, which is between 0.5 and 30 atoms of metal from group VIb per nm² of catalyst, preferably between 2 and 25, more preferably still between 3 and 15. The density of metal from group VIb, expressed as number of atoms of metal from group VI b per unit area of the catalyst (number of atoms of metal from group VIb per nm² of catalyst), is calculated, for example, from the following relationship:

${d\mspace{14mu}{metal}\mspace{14mu}{from}\mspace{14mu}{group}\mspace{14mu}{VIb}} = \frac{\left( {X \times N_{A}} \right)}{\left( {100 \times 10^{18} \times {{??}{\times \left. {??}_{??} \right)}}} \right.}$ with:

-   -   X=% by weight of metal from group VIb;     -   N_(A)=Avogadro's number, equal to 6.022×10²³;     -   S=Specific surface of the catalyst (m²/g), measured according to         the standard ASTM D3663;     -   M_(M)=Molar mass of the metal from group VIb (for example 95.94         g/mol for molybdenum).

For example, if the catalyst contains 20% by weight of molybdenum oxide MoO₃ (i.e. 13.33% by weight of Mo) and has a specific surface of 100 m²/g, the density d(Mo) is equal to:

${d\mspace{14mu}({Mo})} = {\frac{\left( {13.33 \times N_{A}} \right)}{\left( {100 \times 10^{18} \times 100 \times 96} \right)} = {8.4\mspace{14mu}{atoms}\mspace{14mu}{of}\mspace{14mu}{Mo}\text{/}{nm}^{2}\mspace{14mu}{of}\mspace{14mu}{catalyst}}}$

Optionally, the regenerated catalyst of the process according to the invention can additionally exhibit a phosphorus content generally of between 0.3% and 10% by weight of P₂O₅, with respect to the total weight of catalyst, preferably of between 0.5% and 5% by weight, very preferably between 1% and 3% by weight. Furthermore, the phosphorus/(metal from group VIb) molar ratio is generally between 0.1 and 0.7, preferably between 0.2 and 0.6, when phosphorus is present.

Optionally, the regenerated catalyst of the process according to the invention can additionally exhibit, in addition to the coke and sulfur, a low content of contaminants resulting from the feedstock treated by the fresh catalyst from which it originates, such as silicon, arsenic or chlorine.

Preferably, the content of silicon (besides that possibly present on the fresh catalyst) is less than 2% by weight and very preferably less than 1% by weight, with respect to the total weight of the regenerated catalyst.

Preferably, the arsenic content is less than 2000 ppm by weight and very preferably less than 500 ppm by weight, with respect to the total weight of the regenerated catalyst.

Preferably, the chlorine content is less than 2000 ppm by weight and very preferably less than 500 ppm by weight, with respect to the total weight of the regenerated catalyst.

Very preferably, the regenerated catalyst is not contaminated, that is to say contains a content of less than 100 ppm by weight of silicon (besides that possibly present on the fresh catalyst), of less than 50 ppm by weight of arsenic and of less than 50 ppm by weight of chlorine, with respect to the total weight of the regenerated catalyst.

Preferably, the regenerated catalyst of the process according to the invention, in oxide form, is characterized by a specific surface of between 5 and 400 m²/g, preferably of between 10 and 250 m²/g, preferably of between 20 and 200 m²/g, very preferably of between 30 and 180 m²/g. The specific surface is determined in the present invention by the BET method according to the standard ASTM D3663, as described in the work by Rouquerol F., Rouquerol J. and Singh K., Adsorption by Powders & Porous Solids: Principle, Methodology and Applications, Academic Press, 1999, for example by means of an Autopore III™ model device of the Micromeritics™ brand.

The pore volume of the regenerated catalyst is generally between 0.4 cm³/g and 1.3 cm³/g, preferably between 0.6 cm³/g and 1.1 cm³/g. The total pore volume is measured by mercury porosimetry according to the standard ASTM D4284 with a wetting angle of 140°, as described in the same work.

The tapped bulk density (TBD) of the regenerated catalyst is generally between 0.4 and 0.7 g/ml, preferably between 0.45 and 0.69 g/ml. The TBD measurement consists in introducing the catalyst into a measuring cylinder, the volume of which has been determined beforehand, and then, by vibration, in tapping it until a constant volume is obtained. The bulk density of the tapped product is calculated by comparing the mass introduced and the volume occupied after tapping.

This catalyst can be in the form of cylindrical or multilobe (trilobe, quadrilobe, and the like) extrudates with a small diameter, or of spheres.

The oxide support of the regenerated catalyst is usually a porous solid chosen from the group consisting of: aluminas, silica, silica-aluminas and also titanium and magnesium oxides, used alone or as a mixture with alumina or silica-alumina. It is preferably chosen from the group consisting of silica, the family of the transition aluminas and silica-aluminas; very preferably, the oxide support is constituted essentially of at least one transition alumina, that is to say that it comprises at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, indeed even at least 90% by weight, of transition alumina. It preferably consists solely of a transition alumina. Preferably, the oxide support of the regenerated catalyst of the process according to the invention is a “high temperature” transition alumina, that is to say which contains theta-, delta-, kappa- or alpha-phase aluminas, alone or as a mixture, and an amount of less than 20% of gamma-, chi- or eta-phase alumina.

Hydrodesulfurization Process

The hydrodesulfurization process according to the invention consists in bringing the sulfur-containing olefinic gasoline cut into contact with the regenerated catalyst and hydrogen under the following conditions:

-   -   a temperature of between 200° C. and 400° C., preferably of         between 230° C. and 330° C.     -   at a total pressure of between 1 and 3 MPa, preferably of         between 1.5 and 2.5 MPa     -   an hourly space velocity (HSV), defined as being the flow rate         by volume of feedstock relative to the volume of catalyst, of         between 1 and 10 h⁻¹, preferably of between 2 and 6 h⁻¹     -   a hydrogen/gasoline feedstock ratio by volume of between 100 and         1200 SI/I, preferably of between 150 and 400 SI/I.

The hydrodesulfurization process can be carried out in one or more reactors in series of the fixed bed type or of the ebullated bed type. If the process is carried out by means of at least two reactors in series, it is possible to provide a device for the removal of the H₂S from the effluent resulting from the first hydrodesulfurization reactor before treating said effluent in the second hydrodesulfurization reactor.

The hydrodesulfurization process according to the invention is carried out in the presence of a regenerated catalyst. It can also be carried out in the presence of a mixture of a regenerated catalyst and of a fresh catalyst or of a rejuvenated catalyst.

When a fresh or rejuvenated catalyst is present, it comprises at least one metal from group VIII, at least one metal from group VI b and an oxide support, and optionally phosphorus and/or an organic compound such as are described above.

The active phase and the support of the fresh or rejuvenated catalyst may or may not be identical to the active phase and to the support of the regenerated catalyst.

The active phase and the support of the fresh catalyst may or may not be identical to the active phase and to the support of the rejuvenated catalyst.

When the hydrodesulfurization process is carried out in the presence of a regenerated catalyst and of a fresh or rejuvenated catalyst, it can be carried out in a reactor of the fixed bed type containing several catalytic beds.

In this case, and according to a first alternative form, a catalytic bed containing the fresh or rejuvenated catalyst can precede a catalytic bed containing the regenerated catalyst in the direction of the circulation of the feedstock.

In this case, and according to a second alternative form, which is preferred, a catalytic bed containing the regenerated catalyst can precede a catalytic bed containing the fresh or rejuvenated catalyst in the direction of the circulation of the feedstock.

In this case, and according to a third alternative form, a catalytic bed can contain a mixture of a regenerated catalyst and of a fresh catalyst and/or of a rejuvenated catalyst.

In these cases, the operating conditions are those described above. They are generally identical in the different catalytic beds except for the temperature, which generally increases in a catalytic bed following the exothermicity of the hydrodesulfurization reactions.

When the hydrodesulfurization process is carried out in the presence of a regenerated catalyst and of a fresh or rejuvenated catalyst in several reactors in series of the fixed bed type or of the ebullated bed type, one reactor can comprise a regenerated catalyst while another reactor can comprise a fresh or rejuvenated catalyst, or a mixture of a regenerated catalyst and of a fresh and/or rejuvenated catalyst, and this in any order. It is possible to provide a device for the removal of the H₂S from the effluent resulting from the first hydrodesulfurization reactor before treating said effluent in the second reactor.

Selective Hydrogenation (Optional Stage)

According to one alternative form, the gasoline cut is subjected to a selective hydrogenation stage before the hydrodesulfurization process according to the invention.

Preferably, the gasoline treated by the hydrodesulfurization process according to the invention is a heavy gasoline resulting from a distillation stage aimed at separating a broad cut of the gasoline resulting from a cracking process (or FRCN for Full Range Cracked Naphtha) into a light gasoline and a heavy gasoline.

Advantageously, the broad cut FRCN is subjected to a selective hydrogenation stage described below before the distillation stage.

Said FRCN cut is treated beforehand in the presence of hydrogen and of a selective hydrogenation catalyst so as to at least partially hydrogenate the diolefins and to carry out a reaction for increasing the molecular weight of a part of the mercaptan (RSH) compounds present in the feedstock to give thioethers, by reaction with olefins.

To this end, the broad FRCN cut is sent to a selective hydrogenation catalytic reactor containing at least one fixed or moving bed of catalyst for the selective hydrogenation of the diolefins and for increasing the molecular weight of the mercaptans. The reaction for the selective hydrogenation of the diolefins and for increasing the molecular weight of the mercaptans is preferentially carried out on a sulfided catalyst comprising at least one metal from group VIII and optionally at least one metal from group VIb and an oxide support. The metal from group VIII is preferably chosen from nickel and cobalt and in particular nickel. The metal from group VIb, when it is present, is preferably chosen from molybdenum and tungsten and very preferably molybdenum.

The oxide support of the catalyst is preferably chosen from alumina, nickel aluminate, silica, silicon carbide or a mixture of these oxides. Use is preferably made of alumina and more preferably still of high-purity alumina. According to a preferred embodiment, the selective hydrogenation catalyst contains nickel at a content by weight of nickel oxide (in NiO form) of between 1% and 12%, and molybdenum at a content by weight of molybdenum oxide (in MoO₃ form) of between 6% and 18%, with respect to the total weight of the catalyst and a nickel/molybdenum molar ratio of between 0.3 and 2.5, the metals being deposited on a support consisting of alumina and for which the degree of sulfidation of the metals constituting the catalyst being greater than 50%.

During the optional selective hydrogenation stage, gasoline is brought into contact with the catalyst at a temperature of between 50° C. and 250° C., preferably between 80° C. and 220° C. and more preferably still between 90° C. and 200° C., with a liquid space velocity (LHSV) of between 0.5 h⁻¹ and 20 h⁻¹, the unit of the liquid space velocity being the liter of feedstock per liter of catalyst and per hour (l/l·h). The pressure is between 0.4 MPa and 5 MPa, preferably between 0.6 and 4 MPa and more preferably still between 1 and 2 MPa. The optional selective hydrogenation stage is typically carried out with a H₂/gasoline feedstock ratio of between 2 and 100 Sm³ of hydrogen per m³ of feedstock, preferably between 3 and 30 Sm³ of hydrogen per m³ of feedstock.

Sulfidation (Optional Stage)

Before bringing into contact with the feedstock to be treated, the regenerated catalyst of the process according to the invention generally undergoes a sulfidation stage. The sulfidation is preferably carried out in a sulforeducing medium, that is to say in the presence of H₂S and hydrogen, in order to transform metal oxides into sulfides, such as, for example, MoS₂ and Co₉S₈. The sulfidation is carried out by injecting, onto the catalyst, a stream containing H₂S and hydrogen, or else a sulfur compound capable of decomposing to give H₂S in the presence of the catalyst and of hydrogen. Polysulfides, such as dimethyl disulfide (DMDS), are H₂S precursors commonly used to sulfide catalysts. The sulfur can also originate from the feedstock. The temperature is adjusted in order for the H₂S to react with the metal oxides to form metal sulfides. This sulfidation can be carried out in situ or ex situ (inside or outside the reactor) of the reactor of the process according to the invention at temperatures of between 200° C. and 600° C. and more preferentially between 300° C. and 500° C.

EXAMPLES Example 1—Preparation of a Fresh Calcined Catalyst A (Comparative)

The support of the catalyst A is a transition alumina with a specific surface of 140 m²/g and a pore volume of 1.0 cm³/g. The catalyst A is prepared by dry impregnation of the support with an aqueous solution of ammonium heptamolybdate and of cobalt nitrate, the volume of the solution containing the precursors of the metals being strictly equal to the pore volume of the mass of support. The concentration of the metal precursors in aqueous solution is adjusted so as to obtain the desired percentage by weight of molybdenum, cobalt and phosphorus on the final catalyst. After dry impregnation on the support, the catalyst is left to mature for 1 h 30 in a water-saturated chamber, dried under air in an oven at 90° C. for 12 hours and then calcined under air at 450° C. for 2 hours.

The catalyst A obtained after calcination has a content of 15.5% by weight of molybdenum (MoO₃ equivalent) and 3.4% by weight of cobalt (CoO equivalent). This catalyst exhibits a Co/Mo atomic ratio of 0.42.

Example 2—Preparation of a Regenerated Catalyst B (According to the Invention)

The catalyst A is used to desulfurize a catalytic cracking (FCC) gasoline, the characteristics of which are collated in table 1. The reaction is carried out at 270° C. for 900 hours in a reactor of traversed bed type under the following conditions: P=2 MPa, HSV=4 h⁻¹, H₂/HC=300 liters/liters of hydrocarbon feedstock. The catalyst is pretreated at 350° C. with a feedstock containing 4% by weight of sulfur in the DMDS (dimethyl disulfide) form in order to provide the sulfidation of the oxide phases. The reaction takes place in an upward stream in an isothermal pilot reactor.

TABLE 1 Characteristics of the FCC gasoline cut used for the aging of the catalyst A. S ppm 392 Aromatics wt % 41.3 Paraffins wt % 27.2 Naphthenics wt % 11.0 Olefins wt % 20.5 T5° C. 62 T95° C. 225

The spent catalyst A is withdrawn from the reactor on conclusion of the hydrodesulfurization of a catalytic cracking (FCC) gasoline described above. The spent catalyst A is subsequently washed with toluene in a Soxhlet at 250° C. for 7 hours (deoiling).

The regeneration of the spent/washed catalyst A is subsequently carried out in a tubular oven under dry air at 450° C. for 2 hours and the catalyst B is obtained. The residual carbon content of catalyst B is zero. The residual sulfur content is 0.6% by weight, with respect to the weight of the regenerated catalyst.

Example 3—Evaluation of the Catalytic Performance Qualities of the Catalysts A and B

A model feedstock representative of a catalytic cracking (FCC) gasoline containing 10% by weight of 2,3-dimethylbut-2-ene and 0.33% by weight of 3-methylthiophene (i.e. 1000 ppm by weight of sulfur in the feedstock) is used for the evaluation of the catalytic performance qualities of the various catalysts. The solvent used is heptane.

The hydrodesulfurization reaction (HDS) is carried out in a fixed traversed bed reactor under a total pressure of 1.5 MPa, at 210° C., at HSV=6 h⁻¹ (HSV=flow rate by volume of feedstock/volume of catalyst) and an H₂/feedstock ratio by volume of 300 SI/I, in the presence of 4 ml of catalyst. Prior to the HDS reaction, the catalyst is sulfided in situ at 350° C. for 2 hours under a flow of hydrogen containing 15 mol % of H₂S at atmospheric pressure.

Each of the catalysts is placed successively in said reactor. Samples are taken at different time intervals and are analyzed by gas chromatography so as to observe the disappearance of the reactants and the formation of the products.

The catalytic performance qualities of the catalysts are evaluated in terms of catalytic activity and of the selectivity. The hydrodesulfurization (HDS) activity is expressed from the rate constant for the HDS reaction of 3-methylthiophene (kHDS), standardized by the volume of catalyst introduced, and assuming first order kinetics with respect to the sulfur compound. The activity for hydrogenation of the olefins (HydO) is expressed from the rate constant for the hydrogenation reaction of 2,3-dimethylbut-2-ene, standardized by the volume of catalyst introduced, and assuming first order kinetics with respect to the olefin.

The selectivity of the catalyst is expressed by the standardized ratio of the rate constants kHDS/kHydO. The kHDS/kHydO ratio will increase as the catalyst becomes more selective. The values obtained are standardized by taking the catalyst A as reference (relative HDS activity and relative selectivity equal to 100). The performance qualities are thus the relative HDS activity and the relative selectivity (table 2).

TABLE 2 Relative HDS Relative Catalysts activity selectivity A (comparative) 100 100 B (according to the 95 114 invention)

The regenerated catalyst B exhibits a similar activity to the fresh catalyst A and an improved selectivity in hydrodesulfurization with respect to the hydrogenation of olefins with respect to the (fresh calcined) comparative catalysts A.

This improvement in selectivity of the catalysts is particularly advantageous in the case of use in a process for the hydrodesulfurization of gasoline containing olefins for which it is sought to limit as much as possible the loss of octane due to the hydrogenation of the olefins. 

The invention claimed is:
 1. A process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of 200° C. to 400° C., a total pressure of 1 to 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of 1 to 10 h⁻¹ and a hydrogen/gasoline feedstock ratio by volume of 100 to 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, said regenerated catalyst comprises at least one metal from group VIII, at least one metal from group VIb and an oxide support, in which the regenerated catalyst does not undergo addition of metals from groups VIb and/or VIII, of phosphorus and/or of organic compound after regeneration.
 2. The process as claimed in claim 1, in which the regenerated catalyst has a content of metal from group VIb of 1% to 20% by weight of oxide of said metal from group VIb, with respect to the total weight of the regenerated catalyst, and a content of metal from group VIII of 0.1% to 10% by weight of oxide of said metal from group VIII, with respect to the total weight of the regenerated catalyst.
 3. The process as claimed in claim 1, in which the regenerated catalyst additionally contains phosphorus, the phosphorus content being 0.3% to 10% by weight, expressed as P₂O₅, with respect to the total weight of the regenerated catalyst and the phosphorus/(metal from group VIb) molar ratio in the regenerated catalyst is 0.1 to 0.7.
 4. The process as claimed in claim 1, in which, in the regenerated catalyst, the metal from group VIb is tungsten or molybdenum and the metal from group VIII is nickel or cobalt.
 5. The process as claimed in claim 1, in which the regenerated catalyst has a specific surface of 20 to 200 m²/g.
 6. The process as claimed in claim 1, in which the oxide support of the regenerated catalyst is an alumina, silica, a silica-alumina or titanium or magnesium oxides, used alone or as a mixture with an alumina or a silica-alumina.
 7. The process as claimed in claim 1, in which the regenerated catalyst contains residual carbon at a content of less than 2% by weight, with respect to the total weight of the regenerated catalyst.
 8. The process as claimed in claim 1, in which the regenerated catalyst contains sulfur at a content of less than 5% by weight, with respect to the total weight of the regenerated catalyst.
 9. The process as claimed in claim 1, in which the regenerated catalyst is subjected to a sulfidation stage before or during the hydrodesulfurization process.
 10. The process as claimed in claim 1, in which the gasoline cut is a gasoline resulting from a catalytic cracking unit.
 11. The process as claimed in claim 1, in which the regenerated catalyst results from a regeneration stage carried out in an oxygen-containing gas stream carried out at a temperature of 350° C. to 550° C.
 12. The process as claimed in claim 11, in which the regeneration stage is preceded by a deoiling stage which comprises bringing an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut into contact with a stream of inert gas at a temperature of 300° C. to 400° C.
 13. A process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of between 200° C. and 400° C., a total pressure of between 1 and 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of between 1 and 10 h⁻¹ and a hydrogen/gasoline feedstock ratio by volume of between 100 and 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, said regenerated catalyst comprises at least one metal from group VIII, at least one metal from group VIb and an oxide support, which process is carried out in a catalytic bed of a reactor of the fixed bed type containing several catalytic beds; at least one other catalytic bed upstream or downstream of the catalytic bed containing the regenerated catalyst in the direction of the circulation of the feedstock contains at least in part a fresh catalyst and/or a rejuvenated catalyst.
 14. A process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut in which said gasoline cut, hydrogen and a regenerated catalyst are brought into contact, said process being carried out at a temperature of between 200° C. and 400° C., a total pressure of between 1 and 3 MPa, an hourly space velocity, defined as being the flow rate by volume of feedstock relative to the volume of catalyst, of between 1 and 10 h⁻¹ and a hydrogen/gasoline feedstock ratio by volume of between 100 and 1200 SI/I, said regenerated catalyst resulting from an at least partially spent catalyst resulting from a process for the hydrodesulfurization of a sulfur-containing olefinic gasoline cut, said regenerated catalyst comprises at least one metal from group VIII, at least one metal from group VIb and an oxide support, which is carried out in at least two reactors in series of the fixed bed type or of the ebullated bed type; at least one of the reactors contains a regenerated catalyst while another reactor contains a fresh catalyst or a rejuvenated catalyst, or a mixture of a regenerated catalyst and of a fresh and/or rejuvenated catalyst, in any order, with or without removal of at least a part of the H₂S from the effluent resulting from the first reactor before treating said effluent in the second reactor. 